The primary objective was to evaluate acute toxicity (within 10 weeks) associated with increasing hypofractionation to the prostate bed (PB) in post-prostatectomy prostate cancer patients (pts). We hypothesized that escalating the dose per fraction (fx) to the PB in the post-operative setting would have an acceptable toxicity profile.

24 pts with indication for adjuvant or salvage radiotherapy (RT) were enrolled (6 at DLs 1 and 2; 12 at DL 3); all evaluable. Median follow-up was 9.6 months. Median age was 66 years. Median PSA at time of enrollment was 0.06 ng/mL (range <0.03– 0.36 ng/mL). Median time from prostatectomy to enrollment was 8.5 months. 4 pts received concurrent ADT. No G ≥3 GI or GU toxicity was seen at any dose level. GI toxicities and changes in GU toxicity over baseline are summarized (Table 1). 12/24 pts experienced G2 GI toxicity: 2/6 in DL1, 3/6 in DL2 and 7/12 in DL3. All acute G2 GI toxicity resolved. 3/24 patients reported an increase to G1 and G2 GU toxicity following RT in DL1 and DL 2. No patients in DL 3 had increased GU toxicity. At week 2 post-RT, pts reported a decline in the EPIC-26 bowel domain that met criteria for minimally important difference (MID). Rectal QOL declines improved in DLs 1 and 2 by week 10. IPSS scores declined at 2 weeks post-treatment, but improved by 6-10 weeks post-treatment.

Conclusion:

Dose escalation up to 7.1Gy x 5 fractions was completed without G ≥3 toxicity. There was transient G2 rectal toxicity in all dose levels and so the benefit of hypofractionated RT and SBRT should be weighed against this toxicity. Longer follow-up is required to assess late toxicity and disease control. Table 1: Maximum Toxicity by 10 weeks Attributable to RT (number of patients)